Manganese-base alloys



United States Pate 3,230,078 MANGANESE-BASE ALLOYS Alfred William Owen Webb and Norman Bailey, Kent, England, assignors to J. Stone & Company (Propellers) Limited, London, England, a company of Great Britain No Drawing. Filed Jan. 7, 1963, Ser. No. 249,578 4 Claims. (Cl. 75-134) This invention concerns improvements relating to manganese-base alloys. Manganese-copper alloys containing between about and 55% of copper have high damping capacity and a variety of alloys have been developed, based on this binary system, which have useful properties for particular applications.

The possession of a high damping capacity is very desirable in an alloy for marine propellers, but for this purpose the said capacity must be accompanied by sufficiently high strength, fatigue resistance, erosion resistance and corrosion resistance. Also, it must be capable of being melted and cast by the conventional methods by which very large propeller castings are produced. Alloys which have been produced heretofore do not possess all these characteristics together. In general, they are difficult to cast and have inferior mechanical properties in the cast condition.

A series of alloys based on the manganese-copper system and containing aluminium and nickel has now been developed, in which the damping capacity in the cast condition is better than that of the binary alloys, and in which high damping capacity can be obtained Without the need for heat-treatment. These new alloys also have reason- 3,230,078 Patented Jan. 18, 1966 added up to 2.5% without significant change in the cast structure, although the damping capacity falls to some extent. When more than 2.5% of aluminium is added, however, two new phases appear; namely a body-centred cubic phase similar to the beta phase in aluminium bronzes, and a phase believed to be a complex ternary compound Cu Mn Al. When the body-centred cubic phase appears in small amounts, the damping capacity of the alloy increases significantly, while the tensile properties and machineability of the alloy are also improved. The amounts of both of the new phases increase as the aluminium content is raised, but above 6% of aluminium the damping capacity falls once more and the tensile properties of the alloy also deteriorate. Thus alloys containing between 2.5% and 6% of aluminium have exceptionally good damping capacity and tensile properties, and are easier to machine than alloys outside these limits of composition. The presence of aluminium in these amounts also improves the casting characteristics.

The addition of nickel further improves the tensile properties and in conjunction with aluminium also im proves the resistance to corrosion. The addition of nickel has no significant effect on the amounts of the aforesaid body-centred cubic phase and complex ternary compound when added in amounts up to 5%, but it appears to have an influence on the precipitation of alpha-manganese and, if the nickel content exceeds 3.5%, the damping capacity begins to fall rapidly, although below this level nickel appears to have a slightly beneficial effect on damping capacity. The effects of variations in nickel content upon the tensile properties and damping capacity are indicated in Table I.

Table I Chemical Composition, Percent 0.1 0 Youngs Specific Proof Tensile Elonga- Modulus, Damping Stress, Strength, tion, lb/in. Capacity, Manganese Copper l \l u- Nickel Iron Silicon Carbon tons/in. tonsfinfi Percent XlO- Percent mimum able casting characteristics and good mechanical properties.

An alloy in accordance With the present invention contains to of copper, 2.5 to 6% of aluminium and 0.5 to 3.5% of nickel, the rest (except for impurities and incidental constituents) being manganese, which amounts to at least 47%, carbon or silicon present amounting to less than 0.2% respectively. Preferably the manganese content does not exceed 60% and the copper content does not exceed 48%. Iron may be present in amounts up to 5% and tin in amounts up to 2%.

Alloys with such a composition not only possess a high damping capacity and good tensile strength, but may also have a corrosion fatigue resistance greater than that of high tensile brass, which has long been used for marine propellers. For instance, an alloy containing 54.6% of manganese, 36.0% copper, 4.5% of aluminium, 2.1% of nickel, 2.9% of iron, 0.06% of silicon and 0.04% of carbon had an endurance limit in salt spray, based on l0 reversals of stress, of :775 tons/m which compares favourably with values of about :6 tons/in. for accepted propeller alloys.

Binary manganese-copper alloys consist of a matrix of face-centred cubic solid solution containing precipitated particles of alpha-manganese. Aluminium may be The damping capacity values in Table I may be compared with specific damping capacities of 0.3% for a typical high tensile brass, and 10.6% for a cast iron containing about 3.5% of carbon, the latter value being regarded as a good damping capacity.

The damping capacity increases with manganese content up to a maximum at about manganese. On the other hand, tensile properties deteriorate at manganese contents about 60%, and the casting characteristics are also better with alloys of lower manganese content. For instance, the liquidus temperature decreases with decrease in manganese content, the liquidus points of alloys with 70 and 47% of manganese being 1150 and 990 C. respectively, so that it is easier to maintain freedom from oxide inclusions and gas in the case of alloys with lower manganese content. The width of the freezing range is also reduced as the manganese content is lowered, and this reduces the liability of the alloys to shrinkage porosity. Because of this, the most generally useful alloys are likely to have manganese contents close to but slightly below 60%.

The damping capacity is critically dependent upon the silicon and carbon contents, again because they appear to interfere with the form of precipitation of alpha-manganese. If either the silicon content or the carbon content exceeds 0.2%, the damping capacity of the alloy becomes very low, as shown by the following table:

The alloys are also capable of being hot worked by forging and other processes. Such processes can impair vantageous in improving the resistance to impingment corrosion. Its addition is therefore beneficial, except in alloys containing tin, where it should be kept to a very low level.

Other elements may be added for specific known pur- 30 poses, for example lead in amounts up to 1% may be added to ensure a free-machining alloy without impairing either damping capacity or mechanical properties,

Typical tensile properties and damping capacities for Table II I Chemical-Composition, Percent 0.1% Youngs Specific Proof Tensile Elonga- Modulus, Damping Stress, Strength, tion, lb. /in. Capacity, Manganese Copper .alu- Nickel Iron Silicon Carbon tons/i111 tons/in. Percent Percent mlmum Contents of the elements silicon and carbon must, therethe damping capacity, but the alloys are susceptible to fore, never exceed the said limits. Amounts of these heat-treatment, which can be used to restore this capacity. elements in excess of the said limits also harden and em- The improved casting characteristics of the alloys debrittle the alloy and impair its machineability. They also scribed allow the manufacture of sound billets and ingots increase the freezing range, thereby impairing the castfor further working. ability, particularly with alloys having a high manganese This invention comprises also propellers and propeller co ten castings made from alloys having the composition herein- Small addltlons of tin 1mprove the res1stance to corb f set f rth rosion, but in amounts exceeding 2%, tin embrittles the We claim; The Presence P a relafively htfle Fffect 1. A casting having high dam-ping capacity constituted on t e dampmg capaclty or tensfle Propertles, but 15 of an alloy consisting essentially of from 25 to 50% of copper, 2.5 to 6% of aluminium, and 0.5 to 3.5% nickel, the rest being essentially manganese, in an amount of at least 47%, and any carbon and silicon present, as impurities, amounting to less than 0.2%, respectively.

2. A casting as claimed in claim 1, wherein the alloy contains iron in an amount up to 5%.

3. A casting as claimed in claim 1, wherein the alloy contains tin in an amount up to 2%.

alloys in accordance with the invention are given by the 35 A Casting as Claimed in Claim 1, wherein the alloy following table: contains lead in an amount up to 1% Table III Chemical Composition, Percent 0.1% Tensile Elon- Youngs Specific Proof Strength, gation, Modulus, Damping Stress, tons/ Perlb./in. Capacity, Manganese Copper Alu- Nickel Iron Tin Lead. Silicon Carbon tons/in. in. cent l0 Percent mimnm 52. 0 3s. 2 4. 6 2. 1 3. 1 0. 02 1s. 5 40. 2 13. 2 15 52. 6 3s. 1 4. 5 1. 5 3.1 0. 12 17. 4 37.1 34 11. 0 2s 59. 8 30. 7 4. 6 2. 0 2. 9 0. 0s 17. 5 39. 1 30 10. 9 24 49. 6 44. 4 3. 3 1. 5 0. 07 0. 03 17. 0 37. 4 11. 3 19 56. 0 37. 0 4. 8 2. 0 0. 06 0. 14 19. 0 40. 6 20 10. s 21 51. 3 42.1 4.9 1. 6 0. 06 0. 06 17.8 40.6 30 11.7 22 50. 7 39. 9 4. 1 1. 4 3. 2 0. 07 17. 1 35. 3 33 11.2 21 65.4 25.0 4.8 2.1 2.6 0.01 14.4 34.3 42 3.3 30

With such alloys, a high damping capacity can be ob- References Cited by the Examiner tained in the cast condition provided that cooling rates UNITED STATES PATENTS through the temperature range 5O0-3O0 C. are not excessivel fast i.e. are not such as ma occur in the case 2,287,888 6/1942 Kroll -41349 X y y 2,310,094 2/1943 Kroll 75-13 4.9 X

of die castings or other thin walled castings. If necessary, however, the damping capacity of such fast-cooled castings can be improved by heat-treatment within the temperature range 500300 C,

HY LAND BIZOT, Primary Examiner. DAV ll I BECK, Examiner. 

1. A CASTING HAVING HIGH DAMPING CAPACITY CONSTITUTED OF AN ALLOY CONSISTING ESSENTIALLY OF FROM 25 TO 50% OF COPPER, 2.5 TO 6% OF ALUMINUM, AND 0.5 TO 3.5% NICKEL, THE REST BEING ESSENTIALLY MANGANESE, IN AN AMOUNT OF AT LEAST 47%, AND ANY CARBON AND SILICON PRESENT, AS IMPURITIES, AMOUNTING TO LESS THAN 0.2%, RESPECTIVELY. 